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Early PD Diagnosis Smell Test Efficacy Varies by Sex and Race

September 25, 2017

A scratch and sniff test developed by researchers may be able to identify those at greater risk of developing Parkinson disease almost 10 years before diagnosis, but results vary based on participants’ sex and race.

The research article, published in Neurology, suggests that older adults with a poor sense of smell are more likely to develop PD compared with those who scored better on the smell test. Researchers found this association to be stronger in men than in women. This study was also one of a few studies to include black people.

The study by Honglei Chen, MD, PhD, National Institute of Environmental Health Sciences (Research Triangle Park, NC) and colleagues included 1510 white (mean age 75.6 years) and 952 black (75.4 years) participants of the Health, Aging, and Body Composition study. The Brief Smell Identification Test (BSIT) was used to evaluate participants sense of smell between 1999-2000, then researchers retrospectively adjudicated PD cases identified through August 31, 2012, via multiple data sources. The BSIT has people smell 12 common odors including gasoline, soap, lemon, cinnamon and onion, to see if participants can choose the correct answer from four choices.

After data analysis, those who had scored poorly on the smell test were approximately 5 times more likely to develop PD than those found to have a good sense of smell. Specifically, of the 764 participants who scored poorly on the BSIT, 26 developed PD. Of 835 people who scored well on the BSIT, 7 of them developed PD; and out of 863 people who had a medium sense of smell, 9 of them developed PD.

After adjusting for confounding factors associated with developing PD, such as history of head injury, caffeine habits, or nicotine habits, results remained the same. Results showed a strong link between the smell test and PD development up to 6 years later, but beyond 6 years it was not as dependable (doi:10.1212/WNL.0000000000004382).

Dr Chen noted some limitations of the study, however, one being “that not all persons who don’t perform well on the smell test will go on to develop Parkinson’s disease.” Another is that the “inability to perform well on such a test does not rule out other causes for poor smell such as inflammation, tumors or even post-traumatic stress.” In addition, Dr Chen said, “patients were only given a diagnosis at the end of the study, as opposed to earlier time points.  As Parkinson’s may take quite a while to actually diagnose, it’s possible that some patients could have been diagnosed earlier while others may have had other symptoms missed prior to formal diagnosis” (Forbes. September 14, 2017).
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Summing up the value of the study, Dr Paul Wright, Chair, Neurology at North Shore University Hospital (New Hyde Park, NY), said:

“This is an interesting, but limited study that strengthens the notion that especially older men with poor olfaction (smell) are 5.2 times more likely to develop Parkinson’s disease (PD), based on this study….This study showed that there is, however, a racial difference between white and black men where it did show the relationship between PD and decreased smell ability, however it was not statistically significant. This also seemed not to hold true for women.”

Authors said that further research is needed before such a smell test could be used to screen for PD in the general population as it only impacts a small percentage of people.—Amanda Del Signore


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